1. Field of the Invention
The present invention relates to a PCB (printed circuit board), and more particularly, to a PCB having a card slot internally comprising a termination to do impedance matching.
2. Description of the Related Art
Generally, a computer system comprises a main body having a main board to which a plurality of hardware components such as a CPU (central processing unit), a BIOS-ROM (basic input/output system-read only memory) initializing attached devices at the time of booting up the computer system, a RAM (random access memory), a CD-ROM (compact disk-read only memory), a hard disk, etc., are connected.
As shown in FIG. 5, a main board 101 includes card slots 110 to which cards 120 (refer to FIGS. 6A through 6D) such as a memory (RAM) card, a video card, etc. to provide extended capability are inserted, and buses 140 (refer to FIGS. 6A through 6D) through which data signals are transmitted between the card slot 110 and a CPU 130 (refer to FIGS. 6A through 6D). The CPU 130 transmits a high speed digital signal via the buses 140 of the main board 101, and the cards 120 such as the memory (RAM) card, etc., receive the high speed digital signal through the card slots 110 (i.e., as a connecter) connected to the buses 140.
As computer systems use higher speed digital processors, a high frequency (RF) signal employed in the bus also increases. The high frequency signal causes an impedance loss between the card slot 110 and the CPU 130. Thus, to reduce the loss, it is necessary to do impedance matching. The impedance matching is performed by a termination comprising resistors 113 and capacitors 115 which are externally positioned adjacent to the card slots 110 and connected to respective pins of the card slot 110 (see FIG. 5).
As shown in FIGS. 6A through 6D, there are various kinds of terminations, for example, a series connection of the resistor 113 between a power pin (VTT) or ground pin and the respective pin of the card slot 110, a shunt connection of two resistors 113 between the power pin and the respective pin of the card slot 110 and between the ground pin and the respective pin of the card slot 110 a series connection of both the resistor 113 and the capacitor 115 between the ground pin and the respective pin of the card slot 110, etc.
Computer systems can have a small size, thus, reducing component space is advantageous. However, because the conventional termination is fabricated separately from the card slot on the PCB as the main board, the conventional termination occupies a relatively large amount of space on the PCB. Also, a printed circuit is needed to connect the termination and the card slot. Thus, the conventional termination is inconvenient for small computer systems.